Power supplies which provide power to secure data systems, such as audio or digital secure communication systems, must be designed such that data communicated within the secure data system is isolated from the input voltage. Without proper isolation, the data communicated within the secure data system can be detected by monitoring the input voltage or other parameters of the power supply.
A typical prior art secure data system power supply utilizes a flyback converter to convert a DC input voltage into a DC link voltage. The DC link voltage feeds a linear current source which provides a constant current at its output. A shunt voltage regulator coupled to the output of the linear current source provides the output voltage to the secure data system. The linear current source provides the isolation between the secure data system and the remainder of the power supply. The linear current source also sets the power limit for the shunt voltage regulator. Inclusion of the linear current source in the secure data system power supply greatly increases the power consumption of the power supply. Typically, the linear current source accounts for as much as 25% of the losses in the secure data system power supply. Consequently, a secure data system power supply which eliminates the power losses associated with the linear current source would be a significant improvement in that it would reduce the total power requirements of the power supply, and would reduce heat dissipation from the power supply.